There have been many flying toys having rotor which can fly by means of receiving a rotary movement that makes the rotor spin around its center. Such a flying toy has been disclosed in U.S. patent application No. US2002098768 A1 (published on Jul. 25, 2002, inventors: KUO YIN JYH (TW); YANG HSIN-HAO (TW)). Since the rotor of that toy has its blades with fixed elevation angle, so when receiving rotary movement generally with a very high angular speed at the beginning caused by a launcher, the rotor will be effected by a very high lift force that rapidly increases the height of said rotor too much. Concurrent with such a high lift force, an air-drag force effecting on the blades of the rotor is high too, that results in decreasing the rotary speed of the rotor. As a result, the lift force rapidly decreases that in turn makes the rotor fall down. That means the flying rotors having blades with fixed elevation angle will have their flying time relatively short that decreases the amusement effect to players. Moreover, since the flying time of such a flying rotor is too short, so the rotor has not time enough for flying back to its launching position, so-called “boomerang effect”. That further decreases the amusement effect to players.
To overcome the above said problem, some flying toys have recently been developed in the way of changing an elevation angle of the blades according to their rotary speed: reducing the elevation angle of the rotary blades when the rotary speed is high, and increasing the elevation angle of the rotary blades when the rotary speed is low that keeps a sufficient flying time without increasing a flying height too much. Example of such a flying toy has been disclosed in Japanese patent application No. JP2005152090 (published on Jun. 16, 2005, inventor: Masui Hikari (JP)).
However, these toys seem relatively complicated; they need an elevation angle control means for changing the angle according to the rotary speed of the blades.
Therefore, there is still a need for developing flying rotor having blades with changeable elevation angle upon the change of rotary speed of the blades, but with very simple construction, in particular the elevation angle can automatically be changed upon the change of the rotary speed of the blades without any control means.